Realizing this thread is from last year I have been trying to do the same thing with my mac mini/yosemite; reload PS CS3 with the new serial number. Trouble is, I can't find the page that directs me to that number.
I had it running back in 2018 when I loaded the non-activation link, followed all the steps and clicked never registar. But last year I was forced to reformat the drive and lost all that. Using the backup I have the original PS CS3 with the old serial number and no way to locate the new one.
Any thoughts??
Thanks.
Unfortunately CS3 is dead. Adobe killed it off last year. There is no way of activating it and there is no longer any way to install a non-activation version. There are no workarounds.
If you don't have a valid CS4, CS5 or CS6 serial number then a Creative Cloud subscription on a compatible system is your only option from Adobe.